1. Field of the Invention
The present invention relates to an optical packet data switching network. More particularly, the present invention relates to an apparatus and method for transmitting packet data and labels without error in an optical packet data switching network.
2. Description of the Related Art
A general optical packet data switching network is composed of a source node where a sender is located, a relay node where a sender and a receiver are located, and a destination node where a receiver is located. Optical signals generated at the source node are transmitted to the destination node through the relay node or directly transmitted to the destination node.
In the optical packet data switching network, a label, which indicates information about a packet data and a moving direction of the packet data, is transmitted. The label is generated at the source node and transmitted to the relay node, and the relay node updates the received label using a label swapping part. The relay node determines which node is the destination node of the received packet data based on the received label and transmits the K packet data to the determined destination node. A label swapping refers to a process that updates information of the received label about the moving direction of the packet data. The label swapping part updates the information about the moving direction by adding its own information to the received label.
The label is transmitted according to various schemes, for example, a time division multiplexing (TDM), a wavelength division multiplexing (WDM), an optical code division multiplexing (OCDM), a sub-carrier multiplexing (SCM), and an orthogonal optical label.
FIG. 1 is a view explaining the SCM. According to the SCM of FIG. 1, a packet data containing information exists in each wavelength λn (n is a natural number), and carries a label with a sub-carrier at a position away from each wavelength λn as much as ±ƒc and is transmitted together with the label.
The WDM is a scheme that multiplexes plural optical channels having different wavelengths onto a single optical fiber and transmits the channels. According to the WDM, a packet data is transmitted with an odd-numbered wavelength λ2m+1 (m is a positive integer) and a label is carried with an even-numbered wavelength λ2m (m is a positive integer). As described above, according to the WDM, the label is transmitted using an extra wavelength, and thus, an extra optical channel is required to transmit the label. Also, according to the WDM, since the wavelength to transmit the packet data and the wavelength to transmit the label are neighbors to each other, they are not easily divided from each other.
According to the TDM, a label is allocated between a first bit and an eighth bit of a packet data and transmitted. Unlike the WDM and SCM, the TDM requires a packet data processing to obtain label information, and thus, a label swapping process becomes complicated.